1. Field of the Invention
The present invention relates to a configuration for preventing signals of a local oscillator provided to the receiver of a radar device from leaking out from an antenna.
2. Background Information
A pulse radar device finds a target in the surrounding area by sending high-frequency pulse signals produced by a magnetron or other such oscillator out from an antenna, and using the antenna to receive and detect echoes (reflected waves) that come back from the target. The configuration of a conventional radar device is shown in FIG. 3.
As shown in FIG. 3, the receiver 10 of a conventional radar device 1 generally has a configuration in which a front end 3 is provided ahead of a detector 4. The front end 3 converts a high-frequency signal RF received by an antenna 2 down to an intermediate-frequency signal IF. This front end 3 includes a local oscillator 5 that outputs a local oscillation signal LO, and a mixer 6 that mixes the local oscillation signal LO with the received high-frequency signal RF. A receiver including a front end such as this is discussed in Japanese Patent No. 2564074 (Patent Literature 1), Japanese Patent Application Publication No. 2005-337988 (Patent Literature 2), Japanese Patent Application Publication No. S60-197007 (Patent Literature 3), and Japanese Utility Model Application Publication No. H5-2871 (Patent Literature 4), for example.
However, because the magnetron 19 or the local oscillator 5 may become unstable due to temperature changes, they have to be preheated by turning on the power ahead of time, before the transmission and reception of signals. In view of this, a conventional radar device has a mode in which current only flows to the magnetron 19 or the local oscillator 5, and no signals are transmitted or received (hereinafter referred to as a standby mode).
The standby mode has two main roles. The first is to perform preheating by sending current to the magnetron 19 or the local oscillator 5 when the power to the radar device 1 is switched on. Specifically, the magnetron 19 or the local oscillator 5 can be preheated by switching to the standby mode immediately after turning on the power to the radar device 1. Transmission and reception can be carried out properly by starting transmission and reception after first canceling the standby mode after sufficient preheating.
The second role of the standby mode is to continue sending power to the magnetron 19 or the local oscillator 5 while temporarily halting the transmission of pulse signals from the radar antenna 2. For example, if the user wants to halt the transmission and reception of the radar device 1 temporarily, such as when putting in to a harbor, if the supply of electrical power to the magnetron 19 or the local oscillator 5 should be interrupted here, then the preheating will have to be performed again when the transmission and reception are restarted. Therefore, if the system is put in the standby mode when transmission and reception are to be temporarily halted, the transmission and reception can be halted in a state in which power is still being sent to the magnetron 19 or the local oscillator 5. This prevents the magnetron 19 or the local oscillator 5 from becoming unstable due to temperature changes, so transmission and reception can be restarted instantly (without preheating) when necessary.